Bitumen froth can be generated by separating oil sands slurry into a bitumen froth component and a solids-enriched tailings component, which may be performed in a flotation unit. The bitumen froth still includes water and mineral solids that should be removed to meet storage and pipeline criteria. In PFT, a paraffinic solvent is added to the bitumen froth in order to dilute bitumen components and help remove water and mineral solids. Paraffinic solvent acts differently compared to naphthenic solvents, notably in that paraffinic solvents induce precipitation of asphaltenes which form flocs composed of asphaltenes, water and solids. After adding paraffinic solvent to the bitumen froth, the resulting diluted froth can be supplied to a settler vessel that produces a diluted bitumen overflow and a tailings underflow including asphaltenes. While removal of the heavier asphaltene components from the diluted bitumen can have benefits, PFT operations also have number of challenges due to the ability of paraffins to precipitate asphaltenes.
In PFT operations, bitumen froth is diluted with solvent and separated into diluted bitumen and a solvent diluted tailings component in a froth separation unit (FSU), which can include two or three settlers arranged in a counter-current configuration. The diluted bitumen can then be supplied to a solvent recovery unit (SRU) to produce recovered solvent and solvent recovered bitumen, while the solvent diluted tailings component can be supplied to a tailings solvent recovery unit (TSRU) to produce recovered solvent and solvent recovered tailings. The solvent recovered tailings can be further processed or can be supplied to a tailings disposal site for settling.
In the context of PFT operations, there are challenges related to monitoring various streams, components and operational parameters, in order to implement process control strategies. For example, the diluted bitumen should generally include less than 0.1 wt % water and less than 0.1 wt % of fine mineral solids in the diluted bitumen overflow from the FSU. The solvent-to-bitumen (S/B) ratio of the diluted bitumen is also an important parameter that affects asphaltene precipitation and settling characteristics which eventually affects the quality of bitumen product. Variable froth composition and separation unit upsets can increase the likelihood of off-specification streams and can reduce the efficiency of the bitumen extraction process.